Question

In a 100 m dash, Joe runs at a constant velocity of 3.2 m/s for 80 m and then slows to a constant 2 m/s for the remaining distance. What is his average velocity for the entire race? (A) 2.6 m/s ® 2.86 m/s (C) 25 m/s (D) 10 m/s (E) None of the above

please show step by step

Answer 1

Average velocity can be calculated by determining the total displacement divided by the total time of travel

Since we have total displacement = 100 m

we have to calculate the total time of run

Time taken in first 80 m of run

  $T_1 = \frac{Displacement}{Velocity} = \frac{80}{3.2}$

$T_1 = 25 s$

Time taken in last 20 m of run

$T_2 = \frac{20}{2}$

$T_2 = 10 s$

So total time take is

T1 + T2 = 25 +10 = 35 s

So the average velocity is equal to

$V_{avg} = \frac{Total-displacement}{Total-Time}$

$V_{avg} = \frac{100}{35}$

$V_{avg} = 2.86 m/s$

Correct answer is option ( b) 2.86 m/s